UI: Fix settings properties view background

In the Yami theme, the background color in the properties view in the
settings dialog would be incorrect.

UI/data/themes/Yami.qss

@@ -234,6 +234,11 @@ OBSBasicSettings QListWidget::item {
     padding: 6px;
 }
 
+/* Settings properties view */
+OBSBasicSettings #PropertiesContainer {
+    background-color: palette(dark);
+}
+
 /* Dock Widget */
 OBSDock > QWidget {
     background: palette(dark);

UI/properties-view.cpp

@@ -116,6 +116,7 @@ void OBSPropertiesView::RefreshProperties()
 		widget->deleteLater();
 
 	widget = new QWidget();
+	widget->setObjectName("PropertiesContainer");
 
 	QFormLayout *layout = new QFormLayout;
 	layout->setFieldGrowthPolicy(QFormLayout::AllNonFixedFieldsGrow);